Blender viewport and UI lag when external monitor connected
Turbo boost (3,6GHz) only boosts one core. The others sleep, I guess.
So I guess you shouldn't use the boost here. RAM is okay, unless rendering, graphics card isn't used anyway. I use mini-display-port on my System as well, no problem. But im on windows so maybe it's a MAC's problem. Please check out other programs, like Video editing Programs or other comples ones like photoshop. (there are free trials)